SNL arrived at the figures by stripping out deposits housed in "megabranches" with $750 million or more. Those large branches often house large corporate deposits that can skew market share calculations. SNL's numbers are intended to give a better picture of the typical branch performance.

By that measure, Wells Fargo had $553 billion in Main Street deposits, a 9.83 percent market share. Bank of America came in second, with $465 billion or 8.27 percent share.

Including "megabranch" deposits, Bank of America is the largest in the U.S. with $1.1 trillion.

Wells' acquisition of Wachovia propelled it to the top spot, more than doubling its retail deposits and market share from 2007.